GNGTS 2015 - Atti del 34° Convegno Nazionale

On the other side, the HVSRs at Cala Rossa Bay generally become lower than 1 in the frequency range between 1 and 2 Hz. Such an anomaly respect to the Anchor Bay site could be related to the complex network of man-made tunnels and caves within the Lower Pleistocene carbonate grainstones, which could have a disturbing role in seismic wave propagation, leading to an amplification of the ground motion vertical component. Finally, the complex behavior of the HVSRs in the higher frequency range (10-60 Hz) can be related to the vibrational behavior of the dislodged rock blocks. The seismic response observed in frequency from 10 to 60 Hz is in agreement with the results published by Got et al. (2010) showing that the highest seismic energy was concentrated in specific frequency bands depending on geometrical and mechanical properties of the rock blocks. Polarization analyses (Burjánek et al. , 2010, 2012; Galea et al. , 2014) will be carried out in order to derive the main modes of vibration for a better comprehension of the seismic response of the cliff slope as well as of its stability in case of earthquake shaking. Conclusions. Preliminary results of seismic noise measurements carried out in the western part of Cala Rossa Bay (Favignana, Italy) show that a site stratigraphic response exists and is characterized by a HVSR peak between 5 and 6 Hz followed by a dip of the HVSR curve. It was also observed a HVSR dip below level 1 in a narrow frequency range, between 1 and 2 Hz, that could be related to the dense network of man-made tunnels and caves within the Lower Pleistocene carbonate grainstones of the Island. A complex local seismic response was also observed at higher frequencies (10-60 Hz) that can be related to the seismic response of the dislodged rock blocks. The results obtained at Cala Rossa Bay were compared to the ones obtained at Anchor Bay in Malta due to the high similarity of the local geological and lithotechnical setting responsible for ongoing lateral spreading landslide processes. More-detailed studies will be carry out by experiencing analytical approaches devoted to characterize the vibrational modes of the surveyed rock blocks, in order to evaluate the sea cliff stability conditions during earthquake shaking. Acknowledgements. This study is part of a PhD research (Roberto Iannucci) at the Department of Earth Sciences of Sapienza University of Rome. The Authors wish to thank Luca Falconi, Vladimiro Verrubbi and Augusto Screpanti for data and information provided about the Cala Rossa Bay area and Fabio Martorelli for his useful support in the field geological survey. References Abate B., Ferruzza G., Incandela A. and Renda P.; 1995: Tettonica trascorrente nelle Isole Egadi (Sicilia occidentale). Studi Geologici Camerti, vol. spec. 1995/2 , pp. 9-14. Abate B., Incandela A. and Renda P.; 1997: Carta geologica delle isole di Favignana e Levanzo (Arcipelago delle Egadi), Scala 1:12.500. Dip. di Geologia e Geodesia, Università di Palermo. Antonioli F., Kershaw S., Renda P., Rust D., Belluomini G., Cerasoli M., Radtke U. and Silenzi S.; 2006: Elevation of the last interglacial highstand in Sicily (Italy): A benchmark of coastal tectonics. Quaternary International, 145-146 , pp. 3-18. Bard P.Y.; 2005: Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations: measurements, processing, and interpretations. SESAME European Research Project. WP12, deliverable D23.12, 2004, Available at: http://sesame-fp5.obs.ujf-grenoble.fr/Deliverables2004. Bonnefoy-Claudet S., Cotton F. and Bard P.Y.; 2006: The nature of noise wavefield and its applications for site effects studies: a literature review. Earth-Sci. Rev., 79 (3), pp. 205-227. Burjánek J., Gassner-Stamm G., Poggi V., Moore J.R. and Fäh D.; 2010: Ambient vibration analysis of an unstable mountain slope. Geophys. J. Int., 180 (2), pp. 820-828. Burjánek J., Moore J.R., Yugsi Molina F.X. and Fäh D.; 2012: Instrumental evidence of normal mode rock slope vibration. Geophys. J. Int., 188 (2), pp. 559-569. Canuti, P., Casagli, N., Garzonio, C. A. and Vannocci, P.; 1990: Lateral spreads and landslide hazards in the Northern Apennine: the example of M. Fumaiolo (Emilia Romagna) and Chiusi della Verna (Tuscany). Proc. 6th International Congress of the International Association of Engeneering Geology, Amsterdam (Netherlands), August 1990, 3 , pp. 1525-1533. Catalano R., Di Stefano P., Sulli A. and Vitale F.P.; 1996: Paleogeography and structure of the central Mediterranean: Sicily and its offshore area. Tectonophysics, 260 , pp. 291-323. 62 GNGTS 2015 S essione 3.2